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Oil pressure SW on Onan Marquis 7000


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  #1  
Old 10-18-2011, 04:32 PM
Farrout Farrout is offline
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Default Oil pressure SW on Onan Marquis 7000

I have model 7NHMFA26105H Marquis 7000 genset in my RV.
Starts and runs fine for 15-20 minutes then dies and won't restart for an hour or so.
Looking for oil pressure switch, can't find it.
Could it be over heating?

Dennis
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  #2  
Old 10-18-2011, 06:06 PM
Kevin K Kevin K is offline
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Default Re: Oil pressure SW on Marquis 7000

Your oil pressure switch is mounted on the oil filter adapter just above the oil filter. To get to it you will have to remove the top panel, the left side panel where the oil filter is located, and the air duct sheet metal on that side. A wire from the oil filter goes to the control board.

There is no over temperature shutdown on that model.

There are quite a few things that could be causing it to shut down. The first thing I would check is the fuel level in your tank. Your gas cap may be holding a vacuum preventing fuel from reaching the generator. Try unscrewing the gas cap and see if it starts immediately. You may also have a plugged fuel filter on the generator, or a failing fuel pump. Another possibility is a failing ignition module or coil when it gets hot.

The first step is to download a service manual.

http://www.cumminsonan.com/www/pdf/m.../965-0531B.pdf

This is a large file. Please allow time for it to download.
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  #3  
Old 10-22-2011, 02:31 PM
Farrout Farrout is offline
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Default Fuel pump for Onan Marquis 7000 in RV

Thanks for the link to the manual.
I bought an inline fuel filter that I can see the fuel going though and installed just before the carb.

It looks like the fuel is not a constant flow.
How can I find the correct part number for the fuel pump for my generator?

Thanks
Dennis
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Old 10-22-2011, 02:47 PM
Pete Spaco Pete Spaco is offline
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Default Re: Oil pressure SW on Marquis 7000

Before you start replacing things, it would be a good idea to at least try to troubleshoot your way to the problem. First thing I would do is to spray some ether into the intake when the engine quits. If it starts right up, then you can be pretty sure that you have a fuel supply problem, not an ignition or safety circuit problem.
Even then, I think I'd want to check that the fuel lines all the way from the tank are not plugged and that fuel can flow freely through them.
Did you check the amount of fuel in the tank? I have had the situation where floating debris in the tank would get sucked into the fuel intake after running a while. Once there is no more suction from the fuel pump the stuff eventually floats away for a while. Need to see if one can suck fuel from the tank right after it quits if it turns out to be, indeed, a fuel supply problem.


Pete Stanaitis
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Old 10-22-2011, 03:33 PM
Farrout Farrout is offline
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Default Re: Oil pressure SW on Marquis 7000

Thanks for the reply.
I just ran the thing for an hour and it didn't quit.
I'll try the next time I take it out on the road.
I keep my fuel tank above 1/2 full all the time so I don't think it's a low fuel problem.
When it quits, it doesn't start right up. It will start after a few hours.
Is the line to the fuel tank separate from the main engine fuel line?
Just for the record, I have a 1997 Bounder model 32H.

Dennis
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Old 10-22-2011, 03:38 PM
MBB MBB is offline
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Default Re: Oil pressure SW on Marquis 7000

Generally the fuel is sucked from the rv tank but the pickup is much higher then the rv one so the generator can not run the rv out of fuel.
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Old 10-22-2011, 06:29 PM
David C David C is offline
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Default Re: Oil pressure SW on Marquis 7000

You need to determine what part of the combustion process (air, fuel or spark) you are losing. Since it will not start for an hour, it should be alot easier to figure out what is missing. The ones that die and restart in a couple of minutes are the rough ones to diagnose.

As Pete suggested, give it a little shot of ether. If it fires, you are good in the spark and air department. If it doesn't fire, get an old spark plug that is known to be good, open the gap to about an 1/8" and hook it to one of the plug wires, ground the plug and crank. If it will not jump the 1/8" gap, you have an ignition problem. Then you need to check the positive side of the coil for 12 volts, while cranking. If there is no voltage, post back and we will procede from there.

I personally would not add an inline filter between the fuel pump and the carb if it requires the cutting of steel tubing and adding rubber fuel line. A rotten hose would make one heck of a fire.

David C.
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Old 10-22-2011, 09:32 PM
Farrout Farrout is offline
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Default Re: Oil pressure SW on Marquis 7000

On my rig, the line to the carb is a rubber hose, so it didn't require cutting a steel line.

After I get this thing sorted out, I'll run a new piece of fuel hose from the carb to the fuel pump.
I used to work on air cooled VW's, so I am aware of fuel line problems.

Dennis
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Old 11-02-2011, 04:34 PM
Farrout Farrout is offline
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Default Re: Oil pressure SW on Marquis 7000

Latest update on the trouble shooting.
I ran the unit in the driveway for over an hour and it didn't quit.
Closed the compartment door and started driving. It stopped after about 15 minutes.

The next day, I removed the compartment door and ran for about 45 minutes before driving home. The trip home was about an hour. The generator did not stop running.

Not sure what having the compartment door off did. I'll re run the test with door both off and on in a couple of weeks.

Dennis
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Old 11-02-2011, 06:55 PM
Max Thompson Max Thompson is offline
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Default Re: Oil pressure SW on Marquis 7000

Quote:
Originally Posted by Farrout View Post
Latest update on the trouble shooting.
Not sure what having the compartment door off did. Dennis
Let it cool.
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Old 11-02-2011, 08:40 PM
Kevin K Kevin K is offline
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Default Re: Oil pressure SW on Onan Marquis 7000

Does it still take an hour or so to restart when it shuts down?

Just to make sure everyone is on the same page, does it crank OK, but it won't start? Or it won't crank at all until it cools?

It's time, as David C. suggested, to check for spark and fuel.

Pick up an inline spark tester. I like the type with the spark gap, but you can also use the type with the neon bulb. They are only a few dollars. Put it in line with the spark plug you can see when the door is open. Drive around, and when it shuts down, try starting it from the switch on the generator while watching the spark tester. If you see spark and it still doesn't start, you will know the ignition is OK.

If it cranks OK and you have spark, try spraying a shot of carburetor cleaner into the carburetor throat while cranking. If it runs for a few seconds on that, you have lack of fuel.

Being a spec H, I believe your set has an electronic governor. When the governor is not powered up, the throttle is closed. If you can see the governor arm or carburetor throttle linkage, it should move to the open position within 1 or two seconds after you start cranking the engine.
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Old 11-03-2011, 04:44 PM
Farrout Farrout is offline
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Default Re: Oil pressure SW on Onan Marquis 7000

Quote:
Originally Posted by Kevin K View Post
Does it still take an hour or so to restart when it shuts down?

Just to make sure everyone is on the same page, does it crank OK, but it won't start? Or it won't crank at all until it cools?
It's difficult to say how long it takes before it will start after it shuts itself down.

Yes, it does crank but not fire.

Hope to have more information in two weeks after the next trip.
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Old 11-13-2011, 04:10 PM
Farrout Farrout is offline
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Default Re: Oil pressure SW on Onan Marquis 7000

Update.

Took another weekend trip. With door off, generator ran for over an hour with
no problems.
On the way home with the door on, the generator quit after 45 minutes.

One more trip next weekend.

Dennis
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